Hi, I just pushed an update to my Hurd distro build scripts for Fedora 26 at https://github.com/dm0-/gnuxc which also includes a translator for /dev/audio. I've uploaded the translator source separately if anyone else is interested:
https://github.com/dm0-/hurd-rump-audio The README has details, but the summary is that the translator pretends to be a Solaris audio device and acts as a rump kernel client converting I/O to the NetBSD audio device. Since PulseAudio has a Solaris module, this allows audio playback from any programs that use PulseAudio without patching them or modifying their build processes. (That includes IceCat/Firefox, so e.g. web video sites are fully working with this.) Feel free to fork it if it's useful. Thanks. David